1. Field of the Invention
This invention relates to an electric gas blast circuit breaker, and more particularly structural elements for reducing arcing and burning as the breaker contacts open. The invention relates to an electric gas blast circuit breaker of the type having a gas blast device formed by a blast cylinder and a blast piston, having two stationary contact pieces, and having a switching unit movable between closed and open positions for electrically bridging the contact pieces in the closed position and for electrically disconnecting the contact pieces in the open position. In such a circuit breaker, the switching unit includes a tubular supporting body, a slide-contact ring made of arc-resistant material slideably contacting one of the two contact pieces in the closed position, this slide-contact ring being mounted on the supporting body so as to be electrically insulated therefrom, and a plurality of elongated contact elements or contact fingers disposed in the supporting body for electrically connecting the two contact pieces when the switching unit is in the closed position. The contact pieces preferably have a configuration as nozzles at their respective end faces disposed opposite each other.
2. Description of the Prior Art
U.S. Pat. No. 3,789,175 discloses a gas blast circuit breaker of the type above mentioned. In the closed position, the contact surfaces of the contact elements are spring pressed against the cylindrical outside surface of the stationary contact pieces. The electric current flows along the contact elements, and the slide-contact ring is electrically connected to the one contact piece or run-off contact piece. In the closed position, the slide-contact ring is electrically disconnected from the contact elements. Only in the course of the opening motion are the contact elements electrically connected to the slide-contact ring. This will occur immediately prior to the separation of the contact elements from the one stationary contact piece which at this moment is still electrically connected to the slide-contact ring. The contact elements which move radially to the circuit breaker axis will engage a rim projecting from the end face of the slide-contact ring which rim fixedly limits such movement.
In the course of the opening motion, the current must be commutated from the contact elements to the slide-contact ring. In circuit breakers for high normal or short-circuit currents, this commutation may be delayed, when the contact elements slide beyond the stationary contact piece due to the inertia of the contact elements, which are large in cross section. Accordingly, an increased burning may occur on the contact elements. In addition, the metal vapor which will appear during the burning off may affect the contact rating of the circuit breaker.